Here is a patch with a simple box-shadow trick. It is not perfect 'cause the border radius is applied to both sides of the shadow. But it is not so noticeable like the current implementation and needed just some additional lines of code. I feel I could live with it. ;)

If we want a "pixel-perfect" solution :) (without plus rounds) we have to use a :before pseudo-element with a bit more lines of css code.